So fed up, about to buy a carburetor! No 5v

[leeleatherwood]

I am getting sick and tired of this, I just need to get my truck running by now. I have seriously been contemplating a carburetor.

Anyways, I purchased a brand new MS v3 mainboard kit with a MS1 CPU from DIYAutoTune because i was having so much trouble with my last one (accidently fried the CPU hooking up an o2 sensor, upon removing the MS2 CPU one the the pins broke off in the 40pin socket too deep to be removed. Upon replacement of the 40pin socket i wasnt getting tach signal, everything was working fine before that.)

I am not getting 5v at all. No 5v at the 40pin header, no 5v at the proto area and no 5v coming from U5.

I have completed everything in the troubleshooting procedures here except for lifting every resistor (as i have completed the board this is too much work): http://www.megamanual.com/ms2/V3trouble.htm

My power supply is 12v from an ATX PSU.
These are my findings:

+12v on U5 pin closest to DB9
0 resistance between Middle pin U5 and heatsink
0.2mv on U5 pin furthest from DB9

C16 and C17 are correct polarity
+12 on + side of C16, 0v on - side
0v on both sides of C17 is this normal?

D9 installed correctly
+12v on banded side, 0v on other side

C22 correct polarity
0v on both sides of C22 is this normal?

D10, D11, D12 and D13 all correct polarity
12v on banded side of D10, 0v on other side
0v both sides of D11 is this normal?
12v both sides of D12 is this normal?
0v both sides of D13 is this normal?

F1 and F2 installed
Q1 and Q5 Nylon screws
Q9 and Q12 greater than 60ohms resistance between metal tab and heatsink


If i cant get this working by thursday I am going carb and never looking back!

Also my soldering skills are very good, I have been soldering for years and ive never once had a short or a cold joint. Not sayings its not possible but very unlikely.

[DonTZ125]

Just looking at the V3 board schematic, and what you're describing is not only not 'normal', I'd go so far as to say 'not POSSIBLE'. You have 0v at the non-banded end of D10, and 12v at pin 1 of U5?! 12v on both sides of D12 at the same time you have 0v both sides of D13 is very hard to do, since two of those pins are connected not only to each other but to ground.

What you describe would require, IMHO, multiple component failure INCLUDING traces of the board itself.

[leeleatherwood]

Just looking at the V3 board schematic, and what you're describing is not only not 'normal', I'd go so far as to say 'not POSSIBLE'. You have 0v at the non-banded end of D10, and 12v at pin 1 of U5?! 12v on both sides of D12 at the same time you have 0v both sides of D13 is very hard to do, since two of those pins are connected not only to each other but to ground.

What you describe would require, IMHO, multiple component failure INCLUDING traces of the board itself.

Sorry, my notes were wrong, i wrote them down wrong or got confused. I have an EFI4Tuning connector instead of DB37 so i have to test from the bottom on the PCB on that side.

D10 has 12v on both side, correct polarity.
D11 has 12v on banded end, 275mv on other end. Correct polarity.
D12 has 12v on banded end, 0v on other end. Correct polarity.

D13 has 0v on banded end and 275mv on non-banded end. Correct polarity.

Again sorry, Im just so pissed off that I probably wrote stuff down wrong. I just triple checked everything and all else is the same.

[DonTZ125]

Ok, that makes a lot more sense. It sounds like the diodes are good to go; the 275mv between D11 and D13 is probably the Vf for D13. That leaves you with the question of 0v on either side of C17 and C22, and 0.2v coming out of U5.

If C17 is blown (and tant caps do fail - often spectacularly), then yes, you will have basically "ground" along the entire 5v circuit. Try lifting / clipping one lead from C17, and see what that gets you.

[leeleatherwood]

Ok, that makes a lot more sense. It sounds like the diodes are good to go; the 275mv between D11 and D13 is probably the Vf for D13. That leaves you with the question of 0v on either side of C17 and C22, and 0.2v coming out of U5.

If C17 is blown (and tant caps do fail - often spectacularly), then yes, you will have basically "ground" along the entire 5v circuit. Try lifting / clipping one lead from C17, and see what that gets you.

I lifted C17, no change anywhere, Should i replace it? (I have another v3 mainboard that i can scavenge for parts.)

What i dont get, is if U5 is getting the +12v on the left leg and ground in the middle, shouldnt it put out the 5v on the right leg?

Im not an electronics expert by any meens but it seems like the voltage regulator U5 is not functioning if im not even getting 5v out of that.

[DonTZ125]

That was plan 'B'. My thought was that if the cap was blown, it would be shorting out the voltage regulator. Why test that one first? It's easier to lift one leg on the cap than to swap out U5. If nothing happens when you lift C17, then it likely is U5.

[leeleatherwood]

That was plan 'B'. My thought was that if the cap was blown, it would be shorting out the voltage regulator. Why test that one first? It's easier to lift one leg on the cap than to swap out U5. If nothing happens when you lift C17, then it likely is U5.

OK, i will replace U5 and report back.

EDIT: That was it, replaced U5 and now getting 5v at all points!

Thanks, much love!

[DonTZ125]

Glad to hear it!